Hate to say this because I like my car to be flawless but I have had the same problem about 4 times occur since I've owned the car(2005). Could be what you say but it has happend on me so random and seldomly that I never have been able to pinpoint a solution. I have a couple extra iac's laying around if it ever gets worse. My advise is to do buy an iac and keep it handy. I never had any vaccum leaks when this happend to mine, but that is a good thing to check anyways.
chris